Crystalline propylene copolymer compositions having improved sealability and optical properties and reduced solubility

ABSTRACT

Propylene polymer compositions comprising (by weight): A) from 15% to 60% with C 4 -C 8  alpha-olefin(s), containing more than 10%, but less than 14%, of said C 4 -C 8  alpha-olefins (s); B) from 40% to 85% of a copolymer of propylene with C 4 -C 8  alpha-olefin(s), preferably butene, containing from 14% to 30% of said C 4 -C 8  alpha-olefin(s), and optionally from 0.5% to 3% of ethylene; provided that the total content of C 4 -C 8  alpha-olefin(s) in the propylene polymer composition be higher than 10%.

This application is the U.S. national phase of International ApplicationPCT/EP02/11129, filed Oct. 4, 2002.

The present invention relates to crystalline propylene copolymercompositions useful in the preparation of heat-sealable films, sheetsand films thereof and to a process for preparing said compositions.

Crystalline copolymers of propylene with other olefins (mainly ethylene,1-butene or both), or mixtures of such copolymers with other olefinpolymers are known in the prior art as heat-sealable materials.

These crystalline copolymers are obtained by polymerizing propylene withminor amounts of other olefin comonomers in the presence of coordinationcatalysts.

The polymerized comonomer units are statistically distributed in theresulting copolymer and the melting point of said copolymers results tobe lower than the melting point of crystalline propylene homopolymers.Also the seal initiation temperature (as later defined in detail) of thesaid copolymers results to be favorably low.

However, the introduction of the comonomer units adversely affects thecrystal structure of the polymer, resulting in relatively largequantities of a polymer fraction soluble in organic solvents, so thatthe copolymers having a particularly low seal initiation temperaturecannot be used in the field of food packaging.

Many technical solutions are disclosed in the prior art in order to finda good balance between heat-sealability (as demonstrated by low sealinitiation temperatures) and solubility. In particular, publishedEuropean patent application 483523 discloses compositions prepareddirectly in a polymerization process, having a low seal initiationtemperature and a low content of a fraction soluble in xylene at roomtemperature or in n-hexane at 50° C. These compositions comprise (byweight):

-   -   30-60% of a copolymer of propylene and a C₄-C₈ alpha-olefin,        containing 80-98% of propylene;    -   35-70% of a copolymer of propylene with ethylene and optionally        1-10% of a C₄-C₈ alpha-olefin, wherein the content of ethylene        is 5-10% when the C₄-C₈ alpha-olefin is not present, or 0.5-5%        when the C₄-C₈ alpha-olefin is present.

Published European patent application 674991 discloses othercompositions prepared directly in a polymerization process, having agood ink adhesion in addition to a low seal initiation temperature andlow content of a polymer fraction soluble in organic solvents. Thesecompositions comprise (by weight):

-   -   20-60% of a copolymer of propylene with ethylene, containing 1        to 5% of ethylene;    -   40-80% of a copolymer of propylene with ethylene and a C₄-C₈        alpha-olefin, the ethylene content being 1-5% and the C₄-C₈        alpha-olefin content being 6-15%;        the total content of ethylene in the compositions being 1-5% and        the total content of C₄-C₈ alpha-olefin in the compositions        being 2.4-12%.

Other heat-sealable compositions, comprising two different kinds ofcopolymers of propylene with higher alpha-olefins, are disclosed in thepublished European patent application 560326. Such compositions comprise(by weight):

-   -   20-60% of a copolymer of propylene containing 1-10% of a C₄-C₁₀        alpha-olefin;    -   40-80% of a copolymer of propylene containing 15-40% of a C₄-C₁₀        alpha-olefin, in which copolymer the product of multiplying the        content of C₄-C₁₀ alpha-olefin by the content of the copolymer        in the total composition, is equal to or greater than 1200.

In WO 00/11076 heat-sealable compositions with improved properties aredescribed. Such compositions, obtained by degradation of a precursortypically prepared by sequential polymerization, comprise (percent byweight):

-   -   20-80% of one or more propylene copolymers selected from the        group consisting of (i) propylene/ethylene copolymers containing        1-7% of ethylene; (ii) copolymers of propylene with one or more        C₄-C₈ alpha-olefins, containing 2-10% of the C₄-C₈        alpha-olefins; (iii) copolymers of propylene with ethylene and        one or more C₄-C₈ alpha-olefins, containing 0.5-4.5% of ethylene        and 2-6% of C₄-C₈ alpha-olefins, provided that the total content        of ethylene and C₄-C₈ alpha-olefins be equal to or lower than        6.5%;    -   20-80% of one or more propylene copolymers selected from the        group consisting of copolymers of propylene with one or more        C₄-C₈ alpha-olefins, containing from more than 10% to 30% of        C₄-C₈ alpha-olefins, and copolymers of propylene with ethylene        and one or more C₄-C₈ alpha-olefins, containing 1-7% of ethylene        and 6-15% of C₄-C₈ alpha-olefins.

All these technical solutions are tailored in such a way as to have nomore than one component containing more than 10% of C₄-C₈ alpha-olefins.Moreover, when a good ink adhesion is desired, also the total content ofC₄-C₈ alpha-olefins in the compositions is kept relatively low (seeEP-A-674991).

In U.S. Pat. No. 5,948,547 olefin polymer compositions with good levelsof heat-sealability are described, comprising (by weight):

-   -   from 68% to 80% of a statistical copolymer of propylene with        12%-20% of 1-butene and 0%-2% ethylene;    -   from 32% to 20% of a statistical copolymer of propylene with        0%-15% of 1-butene and 1%-8% of ethylene, the two copolymers        being different.

In such document it is explained that lower ethylene contents in thesecond copolymer would result in excessively high sealing temperature.In the examples sealing temperatures higher than 100° C. are reported.

It has now surprisingly been found that a particularly valuable balanceof heat-sealability, low content of a fraction soluble in organicsolvents and optical properties (in particular a very low Haze and highGloss) is obtained when two coplymers containing more than 10% of C₄-C₈alpha-olefins are combined in specific proportions. The high Glossvalues attest to exceptionally good surface properties, in particular avery low stickiness and excellent printability/paintability,notwithstanding the high content in C₄-C₈ alpha-olefins.

Therefore the present invention provides propylene polymer compositionscomprising (by weight):

-   A) from 15% to 60%, preferably from 20% to 60%, more preferably from    20% to 50%, of a copolymer of propylene with C₄-C₈ alpha-olefin(s),    preferably butene, containing more than 10%, preferably 11% or more,    but less than 14%, more preferably up to 13%-13.5%, of said C₄-C₈    alpha-olefin(s);-   B) from 40% to 85%, preferably from 40% to 80%, more preferably from    50% to 80%, of a copolymer of propylene with C₄-C₈ alpha-olefin(s),    preferably butene, containing from 14% to 30%, preferably from 14.5%    to 25%, more preferably from 14.5% to 22%, of said C₄-C₈    alpha-olefin(s), and optionally from 0.5% to 3% of ethylene;    provided that the total content of C₄-C₈ alpha-olefin(s) in the    propylene polymer composition be higher than 10%.

Preferably the total content of C₄-C₈ alpha-olefin(s) in the propylenepolymer composition is equal to or greater than 13%, more preferablygreater than 14.5%, and up to 20%-25%. Preferably the copolymer A) issubstantially free from ethylene.

From the above definitions it is evident that the term “copolymer”includes polymers containing more than one kind of comonomers.

Preferably the Melt Flow Rate (MFR L) values for the compositions of thepresent invention range from 2 to 15 g/10 min., more preferably from 2.5to 10 g/10 min.

The said MFR L values can be obtained directly in polymerization, butpreferably they are obtained by subjecting to degradation a precursorcomposition comprising the same components A) and B) in the above saidproportions, but having WR L values (MFR L (1)) from 0.1 to 5 g/10 min.,preferably from 0.3 to 3 g/10 min., with a ratio MFR L (final) to MFR L(1) of from 2 to 20, preferably from 3 to 15.

As previously said, the compositions of the present invention have lowseal initiation temperatures (preferably lower than 100° C.), a lowcontent of a fraction soluble or extractable in organic solvents(preferably equal to or lower than 20% by weight in xylene at 25° C. andequal to or lower than 6% by weight in n-hexane at 50° C.), very lowhaze values (preferably lower than 1%, more preferably equal to or lowerthan 0.5%, measured on films according to the method described in theexamples), and high gloss values (preferably higher than 85%, measuredon films according to the method described in the examples).

The melting temperature of said composition is preferably from about 125to 140° C.

In particular, the melting temperature of both the total composition andthe component A) is most preferably lower than 135° C., for instancefrom 125 to 134° C.

Moreover, when thermal degradation is to be applied, the compositions ofthe present invention can be obtained by an efficient and inexpensiveprocess (constituting a further object of the present invention),comprising the following stages:

-   1) preparing the previously said precursor composition by    polymerizing the monomers in at least two sequential steps, wherein    components A) and B) are prepared in separate subsequent steps,    operating in each step in the presence of the polymer formed and the    catalyst used in the preceding step, and dosing the molecular weight    regulator (preferably hydrogen) in such amounts as to obtain a MFR    L (1) value for the precursor composition of from 0.1 to 5 g/10    min., preferably from 0.3 to 3 g/10 min.;-   2) subjecting the precursor composition obtained in 1) to a    degradation treatment in order to obtain the desired MFR L (final)    values for the final composition, with a degradation ratio, in terms    of ratio MFR L (final) to MFR L (1), of from 2 to 20, preferably    from 3 to 15.

Such a preferred process is extremely convenient, as it avoids theseparate preparation of the components of the precursor composition andseparate degradation treatments.

From the preceding description it should be clear that in the precursorcomposition the comonomer content and relative amounts of components A)and B) are the same as in the final composition (after degradation). Thedegradation treatment has the effect of increasing the MFR L values ofthe composition from MFR L (1) to MFR L (final), with the said values ofthe ratio between the two MFR L values, namely MFR L (final)/MFR L (1),of from 2 to 20.

The above said MFR L values are measured according to ASTM D 1238 L.

In both the precursor and the final compositions the MFR L values of thecomponents A) and B) are not particularly critical, provided that theMFR L values of the total compositions fall within the said ranges.

Indicatively, the MFR L value of both A) and B) can be from 0.1 to 5g/10 min.

Examples of C₄-C₈ alpha olefins are 1-butene, 1-pentene, 1-hexene,4-methyl-1-pentene and 1-octene. Particularly preferred is 1-butene.

As previously explained, the compositions can be prepared by asequential polymerization, comprising at least two sequential steps,wherein components A) and B) are prepared in separate subsequent steps,operating in each step, except the first step, in the presence of thepolymer formed and the catalyst used in the preceding step. The catalystis added only in the first step, however its activity is such that it isstill active for all the subsequent steps.

The order in which components A) and B) are prepared is not critical.

The polymerization stage, which can be continuous or batch, is carriedout following known techniques and operating in liquid phase, in thepresence or not of inert diluent, or in gas phase, or by mixedliquid-gas techniques. It is preferable to carry out the polymerizationin gas phase.

Reaction time, pressure and temperature relative to the two steps arenot critical, however it is best if the temperature is from 20 to 100°C. The pressure can be atmospheric or higher. The regulation of themolecular weight is carried out by using known regulators, hydrogen inparticular.

Such polymerization is preferably carried out in the presence ofstereospecific Ziegler-Natta catalysts. An essential component of saidcatalysts is a solid catalyst component comprising a titanium compoundhaving at least one titanium-halogen bond, and an electron-donorcompound, both supported on a magnesium halide in active form. Anotheressential component (co-catalyst) is an organoaluminum compound, such asan aluminum alkyl compound.

An external donor is optionally added.

The catalysts generally used in the process of the invention are capableof producing polypropylene with an isotactic index greater than 90%,preferably greater than 95%. Catalysts having the above mentionedcharacteristics are well known in the patent literature; particularlyadvantageous are the catalysts described in U.S. Pat. No. 4,399,054 andEuropean patent 45977.

The solid catalyst components used in said catalysts comprise, aselectron-donors (internal donors), compounds selected from the groupconsisting of ethers, ketones, lactones, compounds containing N, Pand/or S atoms, and esters of mono- and dicarboxylic acids. Particularlysuitable electron-donor compounds are phthalic acid esters, such asdiisobutyl, dioctyl, diphenyl and benzylbutyl phthalate.

Other electron-donors particularly suitable are 1,3-diethers of formula:

wherein R^(I) and R^(II) are the same or different and are C₁-C₁₈ alkyl,C₃-C₁₈ cycloalkyl or C₇-C₁₈ aryl radicals; R^(III) and R^(IV) are thesame or different and are C₁-C₄ alkyl radicals; or are the 1,3-diethersin which the carbon atom in position 2 belongs to a cyclic or polycyclicstructure made up of 5, 6 or 7 carbon atoms and containing two or threeunsaturations. Ethers of this type are described in published Europeanpatent applications 361493 and 728769.

Representative examples of said diethers are2-methyl-2-isopropyl-1,3-dimethoxypropane,2,2-diisobutyl-1,3-dimethoxypropane,2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane,2-isopropyl-2-isoamyl-1,3-dimethoxypropane, 9,9-bis (methoxymethyl)fluorene.

The preparation of the above mentioned catalyst components is carriedout according to various methods.

For example, a MgCl₂.nROH adduct (in particular in the form ofspheroidal particles) wherein n is generally from 1 to 3 and ROH isethanol, butanol or isobutanol, is reacted with an excess of TiCl₄containing the electron-donor compound. The reaction temperature isgenerally from 80 to 120° C. The solid is then isolated and reacted oncemore with TiCl₄, in the presence or absence of the electron-donorcompound, after which it is separated and washed with aliquots of ahydrocarbon until all chlorine ions have disappeared.

In the solid catalyst component the titanium compound, expressed as Ti,is generally present in an amount from 0.5 to 10% by weight. Thequantity of electron-donor compound which remains fixed on the solidcatalyst component generally is 5 to 20% by moles with respect to themagnesium dihalide.

The titanium compounds which can be used for the preparation of thesolid catalyst component are the halides and the halogen alcoholates oftitanium. Titanium tetrachloride is the preferred compound.

The reactions described above result in the formation of a magnesiumhalide in active form. Other reactions are known in the literature,which cause the formation of magnesium halide in active form startingfrom magnesium compounds other than halides, such as magnesiumcarboxylates.

The Al-alkyl compounds used as co-catalysts comprise the Al-trialkyls,such as Al-triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear orcyclic Al-alkyl compounds containing two or more Al atoms bonded to eachother by way of O or N atoms, or SO₄ or SO₃ groups. The Al-alkylcompound is generally used in such a quantity that the Al/Fi ratio befrom 1 to 1000.

The electron-donor compounds that can be used as external donors includearomatic acid esters such as alkyl benzoates, and in particular siliconcompounds containing at least one Si—OR bond, where R is a hydrocarbonradical.

Examples of silicon compounds are (tert-butyl)₂ Si (OCH₃)₂, (cyclohexyl)(methyl) Si (OCH₃)₂, (phenyl)₂ Si (OCH₃)₂ and (cyclopentyl)₂ Si (OCH₃)₂.1,3-diethers having the formulae described above can also be usedadvantageously. If the internal donor is one of these dieters, theexternal donors can be omitted.

The catalysts can be pre-contacted with small amounts of olefins(prepolynerization).

Other catalysts that may be used in the process according to the presentinvention are metallocene-type catalysts, as described in U.S. Pat. No.5,324,800 and EP-A-0 129 368; particularly advantageous are bridgedbis-indenyl metallocenes, for instance as described in U.S. Pat. No.5,145,819 and EP-A-0 485 823. Another class of suitable catalysts arethe so-called constrained geometry catalysts, as described in EP-A-0 416815 (Dow), EP-A-0 420 436 (Exxon), EP-A-0 671 404, EP-A-0 643 066 and WO91/04257. These metallocene compounds may be used to produce thecomponents A) and B).

The degradation treatment, when used, can be carried out by any meansand under the conditions known in the art to be effective in reducingthe molecular weight of olefin polymers.

In particular it is known that the molecular weight of olefin polymerscan be reduced by application of heat (thermal degradation), preferablyin the presence of initiators of free radicals, like ionizing radiationsor chemical initiators.

Particularly preferred among the chemical initiators are the organicperoxides, specific examples of which are 2,5-dimethyl-2,5-di(t-butylperoxy) hexane and dicumyl-peroxide. The degradation treatmentwith the chemical initiators can be carried out in the conventionalapparatuses generally used for processing polymers in the molten state,like in particular single or twin screw extruders. It is preferred tooperate under inert atmosphere, for instance under nitrogen.

The amount of chemical initiator to be added to the precursorcomposition can be easily determined by one skilled in the art, basedupon the MFR L (I) value (i.e. the MFR L value of the precursorcomposition) and the desired MFR L (final) value. Generally such amountis comprised in the range of from 100 to 700 ppm.

The degradation temperature is preferably in the range of from 180 to300° C.

The compositions of the present invention can also contain additivescommonly employed in the art, such as antioxidants, light stabilizers,heat stabilizers, colorants and fillers.

Among the various applications made possible by the previously describedproperties, the compositions of the present invention are particularlyuseful for the preparation of films and sheets.

Films are generally characterized by a thickness of less than 100 μm,while sheets have generally a thickness greater than or equal to 100 μm.

Both films and sheets can be mono- or multilayer.

In the case of multilayer films or sheets, at least one layer comprisesthe compositions of the present invention. Each layer that does notcomprise the compositions of the present invention can be composed ofother olefin polymers, such as polypropylene or polyethylene. Generallyspeaking, the films and sheets of this invention can be prepared byknown techniques, such as extrusion and calendering. Specific examplesof films containing the compositions of the present invention aredisclosed hereinafter in the test for determining the seal initiationtemperature (S.I.T.).

The particulars are given in the following examples, which are given toillustrate, without limiting, the present invention.

EXAMPLES 1-3

In the following Examples precursor compositions are prepared bysequential polymerization, and then subjected to degradation.

The solid catalyst component used in polymerization is a highlystereospecific Ziegler-Natta catalyst component supported on magnesiumchloride, containing about 2.5% by weight of titanium anddiisobutylphthalate as internal donor, prepared by analogy with themethod described in the examples of European published patentapplication 674991.

Catalyst System and Prepolymerization Treatment

Before introducing it into the polymerization reactors, the solidcatalyst component described above is contacted at −5° C. for 5 minuteswith aluminum triethyl (TEAL) and dicyclopentyldimethoxysilane (DCPMS),in a TEAL/DCPMS weight ratio equal to about 4 and in such quantity thatthe TEAL/Ti molar ratio be equal to 65.

The catalyst system is then subjected to prepolymerization bymaintaining it in suspension in liquid propylene at 20° C. for about 20minutes before introducing it into the first polymerization reactor.

Polymerization

Into a first gas phase polymerization reactor a propylene/butenecopolymer (component A)) is produced by feeding in a continuous andconstant flow the prepolymerized catalyst system, hydrogen (used asmolecular weight regulator) and propylene and butene monomers in the gasstate.

Polymerization conditions, molar ratio of the reactants, and compositionof the copolymers obtained are shown in Table 1.

The copolymer produced in the first reactor, constituting 43% by weightof the total composition, is discharged in a continuous flow and, afterhaving been purged of unreacted monomers, is introduced in a continuousflow into a second gas phase reactor, together with quantitativelyconstant flows of hydrogen and propylene, ethylene and 1-butene monomersin the gas state.

The propylene/ethylene/1-butene copolymer formed in the second reactor(component B)) is produced in a quantity equal to 57% by weight withrespect to the total composition. Polymerization conditions, molar ratioof the reactants and composition of the copolymers obtained are shown inTable 1.

The polymer particles exiting the second reactor are subjected to asteam treatment to remove the reactive monomers and volatile substances,and then dried.

Then the polymer particles are introduced in a rotating drum, where theyare mixed with 0.05% by weight of paraffin oil ROL/OB 30 (having adensity of 0.842 kg/l at 20° C. according to ASTM D 1298 and flowingpoint of −10° C. according to ASTM D 97), 0.2% by weight of Irganox B225 (made of about 50% Irganox 1010 and 50% Irgafos 168), 0.05% byweight of calcium stearate and 230 ppm of Luperox 101(2,5-dimethyl-2,5-di (t-butylperoxy) hexane), which acts as initiator offree radicals in the subsequent extrusion treatment. The previously saidIrganox 1010 is pentaerytrityl tetrakis3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate, while Irgafos 168 istris (2,4-di-tert-butylphenyl) phosphite.

Then the polymer particles are introduced in a twin screw extruderBerstorff ZE 25 (length/diameter ratio of screws: 33) and extruded undernitrogen atmosphere in the following conditions:

Rotation speed: 250 rpm; Extruder output: 6-20 kg/hour; Melttemperature: 200-250° C.

The data relating to the polymer compositions so obtained are reportedin Table 1b.

EXAMPLES 4-6

Catalyst system and prepolymerization treatment are the same as inExamples 1-3.

Into a first gas phase polymerization reactor a propylene/butenecopolymer (component A)) is produced by feeding in a continuous andconstant flow the prepolymerized catalyst system, hydrogen (used asmolecular weight regulator) and propylene and butene monomers in the gasstate.

Polymerization conditions, molar ratio of the reactants, and compositionof the copolymers obtained are shown in Table 2.

The copolymer produced in the first reactor, constituting 25% by weightof the total composition in Examples 4 and 5, and 30% of the totalcomposition in Example 6, is discharged in a continuous flow and, afterhaving been purged of unreacted monomers, is introduced in a continuousflow into a second gas phase reactor and then, again in continuous flowand after having been purged of unreacted monomers, in a third gas phasereactor, together with quantitatively constant flows of hydrogen andpropylene, ethylene and 1-butene monomers in the gas state.

The propylene/ethylene/1-butene copolymer formed in the second and thirdreactor (component B)) is produced in a quantity equal to 75% by weightwith respect to the total composition in Examples 4 and 5, and 70% inExample 6.

In detail, the amount of copolymer produced in the second reactor is 50%in Examples 4 and 5, and 40% in Example 6, while the amount of copolymerproduced in the third reactor is 25% in Examples 4 and 5, and 30% inExample 6, always referred to the total composition.

Polymerization conditions, molar ratio of the reactants and compositionof the copolymers obtained are shown in Table 2.

The polymer particles exiting the third reactor are subjected to a steamtreatment to remove the reactive monomers and volatile substances, andthen dried.

The product so obtained is further treated with additives and extrudedusing same additives, additive amounts and conditions as in Examples1-3, except that the amount of Luperox 101 is 250 ppm.

The data relating to the polymer compositions so obtained are reportedin Table 2b.

The data shown in the tables are obtained by using the following testmethods.

-   -   Molar Ratios of the Feed Gases        -   Determined by gas-chromatography.    -   Ethylene and 1-Butene Content of the Polymers        -   Determined by I.R. spectroscopy.    -   Melt Flow Rate MFR L        -   Determined according to ASTM D 1238, condition L.    -   Melting Temperature (Tm) and Crystallization Temperature (Tc)        -   Determined by DSC (Differential Scanning Calorimetry).    -   Xylene Soluble Fraction        -   Determined as follows.        -   2.5 g of polymer and 250 cm³ of xylene are introduced in a            glass flask equipped with a refrigerator and a magnetical            stirrer. The temperature is raised in 30 minutes up to the            boiling point of the solvent. The so obtained clear solution            is then kept under reflux and stirring for further 30            minutes. The closed flask is then kept for 30 minutes in a            bath of ice and water and in thermostatic water bath at            25° C. for 30 minutes as well. The so formed solid is            filtered on quick filtering paper. 100 cm³ of the filtered            liquid is poured in a previously weighed aluminum container            which is heated on a heating plate under nitrogen flow, to            remove the solvent by evaporation. The container is then            kept in an oven at 80° C. under vacuum until constant weight            is obtained.    -   Hexane Soluble Fraction        -   Determined according to FDA 177, 1520, by suspending in an            excess of hexane a 100 μm thick film specimen of the            composition being analyzed, in an autoclave at 50° C. for 2            hours. Then the hexane is removed by evaporation and the            dried residue is weighed.    -   Seal Initiation Temperature (S.I.T.)        -   Determined as follows.    -   Preparation of the Film Specimens        -   Some films with a thickness of 50 μm are prepared by            extruding each test composition in a single screw Collin            extruder (length/diameter ratio of screw: 25) at a film            drawing speed of 7 m/min. and a melt temperature of            210-250° C. Each resulting film is superimposed on a 1000 μm            thick film of a propylene homopolymer having an isotacticity            index of 97 and a MFR L of 2 g/10 min. The superimposed            films are bonded to each other in a Carver press at 200° C.            under a 9000 kg load, which is maintained for 5 minutes.        -   The resulting laminates are stretched longitudinally and            transversally, i.e. biaxially, by a factor 6 with a TM Long            film stretcher at 150° C., thus obtaining a 20 μm thick film            (18 μm homopolymer+2 μm test composition).        -   2×5 cm specimens are cut from the films.    -   Determination of the S.I.T.    -   For each test two of the above specimens are superimposed in        alignment, the adjacent layers being layers of the particular        test composition. The superimposed specimens are sealed along        one of the 5 cm sides with a Brugger Feinmechanik Sealer, model        HSG-ETK 745. Sealing time is 0.5 seconds at a pressure of 0.1        N/mm². The sealing temperature is increased for each seal,        starting from about 10° C. less than the melting temperature of        the test composition. The sealed samples are left to cool and        then their unsealed ends are attached to an Instron machine        where they are tested at a traction speed of 50 mm/min.        -   The S.I.T. is the minimum sealing temperature at which the            seal does not break when a load of at least 2 Newtons is            applied in the said test conditions.    -   Haze on Film        -   Determined on 50 μm thick films of the test composition,            prepared as described for the S.I.T. test. The measurement            is carried out on a 50×50 mm portion cut from the central            zone of the film.        -   The instrument used for the test is a Gardner photometer            with Haze-meter UX-10 equipped with a G.E. 1209 lamp and            filter C. The instrument calibration is made by carrying out            a measurement in the absence of the sample (0% Haze) and a            measurement with intercepted light beam (100% Haze).    -   Gloss on Film        -   Determined on the same specimens as for the Haze.        -   The instrument used for the test is a model 1020 Zehntner            photometer for incident measurements. The calibration is            made by carrying out a measurement at incidence angle of 60°            on black glass having a standard Gloss of 96.2% and a            measurement at an incidence angle of 45° on black glass            having a standard Gloss of 55.4%.

TABLE 1 EXAMPLES 1 2 3 1^(st) REACTOR Temperature, ° C. 65 65 65Pressure, MPa 14 14 14 H₂/C₃ ⁻, mol. 0.006 0.006 0.006 C₄ ⁻/C₄ ⁻ + C₃ ⁻,mol. 0.2 0.2 0.2 RESULTING POLYMER C₄ ⁻, % 12 12.2 12.1 MFR L, g/10 min.1.8 2.4 2.1 2^(nd) REACTOR Temperature, ° C. 70 70 70 Pressure, MPa 1414 14 H₂/C₃ ⁻, mol. 0.005 0.005 0.005 C₂ ⁻/C₂ ⁻ + C₃ ⁻, mol. 0.01 0.010.01 C₄ ⁻/C₄ ⁻ + C₃ ⁻, mol. 0.25 0.27 0.27 RESULTING POLYMER C₂ ⁻, % 1.51.05 1.2 C₄ ⁻, % 15.3 18.0 18.7 TOTAL COMPOSITION C₂ ⁻, % 0.85 0.6 0.7C₄ ⁻, % 13.9 15.5 15.85 MFR L, g/10 min. 1.1 1.03 1.2

TABLE 1 b EXAMPLES 1 2 3 MFR L, g/10 min. 5.8 5.4 5.8 X.I., % 88.8 84.384.3 H.S., % 3.1 4.7 5 X.S. I.V., dl/g 1.89 1.77 1.77 Tm, ° C. 135 132133 Tc, ° C. 87 83 81 S.I.T., ° C. 103 95 95 Haze, % 0.37 — 0.2 Gloss, ‰90.4 — 91

TABLE 2 EXAMPLES 4 5 6 1^(st) REACTOR Temperature, ° C. 67 67 67Pressure, MPa 14 14 14 H₂/C₃ ⁻, mol. 0.007 0.006 0.007 C₄ ⁻/C₄ ⁻ + C₃ ⁻,mol. 0.2 0.2 0.2 RESULTING POLYMER C₄ ⁻, % 12 12.2 12.1 MFR L, g/10 min.2.9 2.2 2.9 2^(nd) REACTOR Temperature, ° C. 70 70 70 Pressure, MPa 1414 14 H₂/C₃ ⁻, mol. 0.004 0.004 0.005 C₂ ⁻/C₂ ⁻ + C₃ ⁻, mol. 0.00820.0082 0.0082 C₄ ⁻/C₄ ⁻ + C₃ ⁻, mol. 0.26 0.26 0.26 RESULTING POLYMER C₂⁻, % 1.07 0.93 1 C₄ ⁻, % 16 16.6 16 3^(rd) REACTOR Temperature, ° C. 6565 65 Pressure, MPa 14 14 14 H₂/C₃ ⁻, mol. 0.004 0.004 0.003 C₂ ⁻/C₂ ⁻ +C₃ ⁻, mol. 0.010 0.010 0.010 C₄ ⁻/C₄ ⁻ + C₃ ⁻, mol. 0.26 0.26 0.26RESULTING POLYMER C₂ ⁻, % 1.07 0.93 1 C₄ ⁻% 16 16.6 16 TOTAL COMPOSITIONC₂ ⁻, %, 0.8 0.7 0.7 C₄ ⁻, % 15 15.5 14.8 MFR L, g/10 min. 0.96 0.950.77

TABLE 2b EXAMPLES 4 5 6 MFR L, g/10 min. 4.3 4.4 5.8 X.I., % 89.2 90.291.5 H.S., % 5.4 5.7 4.6 X.S. I.V., dl/g 1.4 1.44 1.38 Tm, ° C. 127 127128.8 Tc, ° C. 81 83 84.96 S.I.T., ° C. 93 93 95 Haze, % 0.2 0.3 0.2Gloss, ‰ 91 90 90 Note to the tables: C₂ ⁻ = ethylene; C₃ ⁻ = propylene;C₄ ⁻ = 1-butene; X.I. = Xylene Insoluble fraction; H.S. = Hexane Solublefraction; X.S. I.V. = Intrinsic Viscosity of Xilene Soluble fraction;all percent amounts (except for Haze) are by weight.

1. Propylene polymer compositions comprising (by weight): A) from 20% to50% of a copolymer of propylene with C₄-C₈ alpha-olefin(s), containingfrom 11% to less than 14%, of said C₄-C₈ alpha-olefin(s); and B) from50% to 80% of a copolymer of propylene with C₄-C₈ alpha-olefin(s),containing from 14% to 30% of said C₄-C₈ alpha-olefin(s), and optionallyfrom 0.5% to 3% of ethylene.
 2. The propylene polymer compositions ofclaim 1, wherein the total content of C₄-C₈ alpha-olefin(s) is at least13%.
 3. The propylene polymer compositions of claim 1, having MFR Lvalues from 2 to 15 g/10 min.
 4. A propylene polymer compositionobtained by subjecting a precursor composition having an MFR L (1) offrom 0.1 to 5 g/10 min, comprising (by weight): A) from 20% to 50% of acopolymer of propylene with C₄-C₈ alpha-olefin(s), containing from 11%to less than 14%, of said C₄-C₈ alpha-olefin(s); and B) from 50% to 80%of a copolymer of propylene with C₄-C₈ alpha-olefin(s), containing from14% to 30% of said C₄-C₈ alpha-olefin(s), and optionally from 0.5% to 3%of ethylene; to degradation, thereby producing an MFR L, wherein a ratioMFR L to MFR L (1) is from 2 to
 20. 5. A process for preparing propylenepolymer compositions comprising the following stages: 1) preparing aprecursor composition having an MFR L (1) of from 0.1 to 5 g/10 min.comprising (by weight): A) from 20% to 50% of a copolymer of propylenewith C₄-C₈ alpha-olefin(s), containing from 11%, to less than 14%, ofsaid C₄-C₈ alpha-olefin(s); and B) from 50% to 80% of a copolymer ofpropylene with C₄-C₈ alpha-olefin(s), containing from 14% to 30% of saidC₄-C₈ alpha-olefin(s), and optionally from 0.5% to 3% of ethylene; bypolymerizing the monomers in at least two sequential steps, whereincomponents A) and B) are prepared in separate subsequent steps,operating in each step in the presence of the polymer formed and thecatalyst used in the preceding step; and 2) subjecting the precursorcomposition obtained in 1) to a degradation treatment, thereby obtaininga MFR L of 2-15, wherein a ratio MFR L to MFR L (1), is from 2 to
 20. 6.A propylene polymer composition comprising (by weight): A) from 20% to50% of a copolymer of propylene with C₄-C₈ alpha-olefin(s), containingfrom 11% to less than 14%, of said C₄-C₈ alpha-olefin(s); B) from 50% to80% of a copolymer of propylene with C₄-C₈ alpha-olefin(s), containingfrom 14% to 30% of said C₄-C₈ alpha-olefin(s), and optionally from 0.5%to 3% of ethylene; and a fraction soluble in xylene of at most 20% byweight.
 7. A propylene polymer composition obtained by subjecting aprecursor composition having an MFR L (1) of from 0.1 to 5 g/10 min,comprising (by weight): A) from 20% to 50% of a copolymer of propylenewith C₄-C₈ alpha-olefin(s), containing from 11% to less than 14%, ofsaid C₄-C₈ alpha-olefin(s); and B) from 50% to 80% of a copolymer ofpropylene with C₄-C₈ alpha-olefin(s), containing from 14% to 30% of saidC₄-C₈ alpha-olefin(s), and optionally from 0.5% to 3% of ethylene; todegradation, thereby producing an MFR L, wherein a ratio MFR L to MFR L(1) is from 2 to 20, the propylene polymer composition comprising afraction soluble in xylene of at most 20% by weight.
 8. A process forpreparing propylene polymer compositions comprising the followingstages: 1) preparing a precursor composition having an MFR L (1) of from0.1 to 5 g/10 min. comprising (by weight): A) from 20% to 50% of acopolymer of propylene with C₄-C₈ alpha-olefin(s), containing from 11%to less than 14%, of said C₄-C₈ alpha-olefin(s); and B) from 50% to 80%of a copolymer of propylene with C₄-C₈ alpha-olefin(s), containing from14% to 30% of said C₄-C₈ alpha-olefin(s), and optionally from 0.5% to 3%of ethylene; by polymerizing the monomers in at least two sequentialsteps, wherein components A) and B) are prepared in separate subsequentsteps, operating in each step in the presence of the polymer formed andthe catalyst used in the preceding step; and 2) subjecting the precursorcomposition obtained in 1) to a degradation treatment, thereby obtaininga MFR L of 2-15, wherein a ratio MFR L to MFR L (1), is from 2 to 20,wherein the propylene polymer composition comprises a fraction solublein xylene of at most 20% by weight.
 9. The propylene polymer compositionof claim 6 further comprising a haze value lower than 1% measured on a50 μm thick film comprising the propylene polymer composition.
 10. Thepropylene polymer composition of claim 7 further comprising a haze valuelower than 1% measured on a 50 μm thick film comprising the propylenepolymer composition.
 11. The process of claim 8 further comprising ahaze value of the propylene polymer composition lower than 1% measuredon a 50 μm film comprising the propylene polymer composition.